ito na experience ko, kapag nasa lapag yung amp, we hear bassier tone dahil sa pagdaan ng tunog sa flooring. Might be good kung yun ang gusto mo i-capture ng instrument microphone na i-feed to PA.
that's called the
bass coupling effect. 
the problem is most ampstands take your amp off the floor, kaya numinipis ang tunog. Opay21's ampstand keeps the amp on the floor, maximizing bass definition. Siyempre the bass is a little less than if the amp is on the totally on the floor, because now it's only the rear edge on the ground.
yung tinis ng nariring niya ay dahil sa directionality ng high frequencies ng tunog niya. simply speaking, the high frequencies are greatest when you are "on-axis" with speaker (read:directly in front of it), then they roll-off the further off-axis you get. This is why when you are standing off to the side of your amp, maganda ang tunog, pero when you bend down to listen, masakit, matalas yung tunog. Kaya minsan akala mo ang ganda ng tunog mo pero pag tingin mo sa mesa sa harap, walang naka-upo.
All guitar amps do this. 4x12's are more directional than 1x12's, and closedback cabs are more directional than openbacks.
the main problem is getting the sound you hear to be as close as possible to the sound that the audience hears.
Weber Beam Blockers were invented to address that. also, google "Mitchell doughnuts".
amp stands help by simply dispersing the sound a little more evenly throughout the venue (kung maliit yung venue, like saguijo, route 196 etc). Also what you will hear from a tilted amp is also VERY close to what a mic will pick up. so if you hear the excess treble, roll it down.
BTW whether or not the amp is on the floor, pareho parin ang mapi-pickup ng mic na tunog (kung close-miked ha). The added bass you hear is just for the sound perception on stage.
