increased perceived hop bitterness with rye???

I have no idea what it could be.  The OP says, beyond all doubt, the only difference between the 2 beers is the Rye. So, I guess it’s the Rye.  I’m not dying on this hill.  ;D

Not that this has anything to do with the OP and the Scottish Ale, but interestingly, Brulosophy did an experiment that is on-point to this conversation.  And they did find a difference between a beer made with Rye and one with not.  No mention of increased bitterness, but reading between the lines, I can see where one can get “spicy” from Rye.

glad to know this. Its a lingering bitterness on the finish, not unpleasant, just not expected.

Bitterness or dryness?

bitterness, tbh, it tastes slightly fuller bodied than it normally does, although not to a great extent.

The first thing I thought was “taste receptors?” and the second was that this sounds like an interesting brewing experiment. I definitely pick up the peppery quality of rye whether I’m brewing or baking with it.