Wagit, the problem is that we DON'T have an AoA indicator. Wish we did. The ASI is the next best thing.
During training any reference to Blue Line should always be a qualified one, with an allowance for any change from the relevent conditions.
The next step is to have some idea of how Vyse changes & use that. An easy way is check the manual & see what it is at altitude. The change isn't linear but close enough so a rate of change with altitude can be found eg 2kts / 1000' or whatever.