Lie makes a difference for sure. If it's the same lie, I've tested both measuring and cutting to match heel to end of stick and standing tall. Like you said, blade length does affect standing length.
Unfortunately from my experience it just depends how it feels overall since there so many variables when it comes to changing and trying different curve patterns. For me, even a 1/4" difference in the exact same stick and curve affects how I stickhandle. I wish I wasn't so sensitive to such a small change. 😔.
My advice is to be on the safe side and leave the new curve a bit longer than what you have and slowly cut it shorter and shorter until it feels comfortable, but the reality is that regardless whether it's the "right" height, there will be an overall adjustment period with the new curve due to lie, rocker, toe shape, overall curve shape differences.
I personally have a hard time getting used to blades that don't have the same rocker as the p28. I love the versatility of the blade shape and rocker. I think my ideal blade would be a p28 shape with a Hossa pro curve. I really like the hossa pro but wish it had more rocker.