You're welcome!

No, it means a lower HF corner (IOW less BW for a given Fc), less acoustic power, ergo lower throat distortion which can actually increase efficiency down around Fc because it's not being 'squeezed' hard. Choosing XO point/slopes is a balancing act of trade-offs of which the horn's mass corner can be one of them. Not being familiar with MSL-4 beyond its published data, it's 800 Hz XO point doesn't seem all that low considering its 65 Hz F4.

Not sure what you mean by 'smoothing guide' since with a