Steve,

I assume you are refering to Graflite reflectors. I've had the same thought but always end up just using 5/25 bulbs with the small reflectors and 11/22 with the large reflector. Flash calculations invovle many variables and can get complex so experimentation/experience seems the best answer... of which I have NONE when it comes to mixing/matching bulbs and reflectors.

I also am wedded to my collection of old Kodak Professional and Master Photoguides because of their handy flash calculators and rely on them as I think through flash bulb applications.

Here are some numbers to think about from the 1977 Professional Photoguide:

25B bulb @ 100 ASA for deep reflector (4 - 6 inch) - GN = 175
25B bulb @ 100 ASA for shallow reflector (4 - 8 inch) - GN = 120

In my kind of arithmatic I'd open 1 stop if using the 7 inch reflector vs the 5 inch with a 25B (for example) bulb.

Take this with a grain o'salt since it's purely an academic comment with no exeprience or success to justify it!