Hi, no issues with that harness for Salty and he PULLS!
Definitely the perfect fit was the best of all I have tried by far
I did have to 'modify' the harness a bit as the small underside part still gave too long a length between the T and the V under his neck so the latter rose p too much and hit his neck - I simply tied a bit of rope to bypass the non-adjustable webbing there and tightened it a bit
The above doesn't seem to be the case for you, but can you go to a shop and make sure its actually the 'best fit'?
Perhaps its a bit loose under the tum?
I now run the (extendable) lead forwards through the back ring (like a fairlead on a boat), over his left shoulder and then clip it onto the chest ring
I walk with him on my right side. I know this is opposite side to what I was expecting to work, but it is better with him.
In fact I am amazed at the difference between this and having separate lead ends to chest and back rings
Worth a try?
All above just thoughts.
YMMV, I dont know what I am doing, etc