I always use small boxes like here with BG20 from Visaton.
I also checked my measurements at 30, 40, 50cm distance and my work with dsp and measurement was always in listening tests with own recorded instruments them playing against the box making me content
I have them running on a 50w class AB amp currently. Seems to handle well. But I don't have them flexing their excursion as I have them limited to about 100hz before I integrate a sub. So I imagine the design and bandwidth you run it at will matter for power handling. It'll handle power, but I'm not sure how much before you get lots of distortion, etc.
Very best,
These are rated at 40W RMS. It should be OK with a lower powered guitar amp. Keep in mind there usually isn’t any compression or safety limiting on guitar amps, they can produce large peaks of output. It would be perfect for a practice amp or acoustic where you want a clean sound.