I also think it's odd that the front and rear don't roll round to the same degree. I think it'd handle better with a 180 on the back, the 190 (and consequent flatter profile) doesn't roll over with the front in the right way.
In the 90's I helped a mate turn his Kawasaki Zephyr 1100 into a national show winning Streetfighter.
The budget to do so kept growing & growing. To the point it basically became a blank cheque.
One of the upgrades he insisted on was a 200 section (or bigger) rear tyre.
After a lot of beer mat maths. I proved to him on paper that it would bollox up the handling. Mainly due to what you're experiencing Chas. Plus the fact we'd changed the swingarm from a twin shock to a mono shock & were using a Fireblade shock on it. A better quality shock, but designed for a much lighter bike.
However, he wouldn't listen & got exactly what he requested.
A radical looking bike with various parts reassigned from the top sports bikes of the day plus a load of one-off bits.
That looked great, but handled like a pi$$ed up pig on rollerskates!