Found out a little bit more about Tarvie Lodge/Tarvie House. Attached an image of an historical environment record of the estate. It shows this info about what was contained on the estate. The info is quite minimal but it gives a general idea.
"Site Type: FARMSTEAD, SHEEP FOLD, LIME KILN, HEAD DYKE, HUNTING LODGE
Council: Perth and Kinross"Taken from
pastmap
Found a more up to date architect's site regarding demolishing the shooting lodge and building a new house over it. It was apparently completed in 2015.
Slightly better than the other design was, but still, in my opinion, doesn't suit the surroundings.
http://cameronwebster.com/project/tarvie-shooting-lodge/There is some slight background information here on Tarvie Lodge, but not much.
Now I'm not sure when the original Tarvie Lodge was built but it doesn't "seem" from the time Leonard Small and Margaret Robertson had my 4x great grandfather, Leonard there (1773). It seems too Victorian. Can't seem to find much about the house anywhere online except for the odd picture here and there.
Here is another picture of what Tarvie Lodge was like;
http://tour-scotland-photographs.blogspot.co.uk/2015/04/old-photograph-tarvie-lodge-enochdhu.htmlAnyone know anything about buildings to know when it was roughly built
I have a birth record for one of Leonard's (b.1773) siblings. Anne Small b.1771. The residence was stated as Tarvie then.
This is something I came across regarding one of Leonard's brother's -
A Patrick Peter Small b.1782https://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=48623544Can't seem to find anything on SP regarding his marriage mentioned in that link to Isobell Rattray
(there's that Rattray name again!).
However I've found a birth for an
Isabella Rattray Small b. 7th February 1822 in Longforgan, parents stated as Peter Small and Isobell Rattray. Whether or not Peter is Patrick

I'm a bit dubious about Patrick Peter due to finding this on ancestry. Take much of it with a grain of salt really and just use it as a base to start searching on SP and/or other sites. However it has been useful in many ways.
Now on the ongoing quest to finding a potential link to The Smalls of Dirnanean. I have a feeling this will all prove fruitless due to the lack of records starting at
Patrick Small b.1750 and going back from there.
Now, what do we know?
- My 4x Great-Grandfather Leonard was born at Tarvie, Moulin to Patrick Small and Margaret Robertson.
Tarvie is only a small distance from Dirnanean, Straloch and Kindrogan. Straloch is mentioned on Wikipedia here: https://en.wikipedia.org/wiki/James_Small_(Scottish_factor) "James Small was a member of the Smalls of Dirnanean and the Robertsons of Straloch"
Tarvie could be Robertson lands?
See the distance in the image below. Basically neighbours.

A Patrick William Small lived in Glenisla in the 1800s with his wife Amelia Rattray. He was a local landowner. There was a monument built in Glenisla to commemorate him. See Wikipedia here: https://en.wikipedia.org/wiki/Kirkton_of_Glenisla Also Find a grave: https://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=76771964
In the newspaper clippings attached to the find a grave entry above it mentions that there are various branches of Smalls throughout Perthshire.
This is Patrick William Small's son James, who also has a memorial; https://en.wikipedia.org/wiki/James_Small_(Scottish_laird)
Around 1808 I believe my 4x gt-grandfather Leonard to be living in Glenisla. He married a Jannet McKenzie in 1808 before marrying my 4x gt-grandmother. Jannet must have died before this. Can't find any record of her death though.
Findlay Small b.1809 was Leonard and Jannet's first child. He was born in Glenisla.
Margaret Small b. 1811 was born in Glenisla also. This was Jannet's last child. Leonard doesn't have another child until 1827, this time Airlie, Angus. So he has moved after I presume Jannet died.
What does this all tell me? Nothing concrete that's for sure. But, given the time period and locations I feel there just HAS to be a link to Dirnanean somewhere. Finding that link though, impossible. It must be further back.
Tarvie, Straloch, Glenisla, Moulin, Kirkmichael, The name Patrick occurring in my branch repeatedly, marrying Robertsons and Rattrays. The signs all point there. 
Perhaps I'm reaching, but this is just a feeling, and and a pretty strong one.