In MVP increasing the SVR decreasing LV emptying, leading to a fuller Left-Ventricle on the next filling. This fuller ventricle makes the chordae attached to the valve more taut and prevents the valves from prolapsing. That's the way I remember it at least.
Exactly. MVP is a regurgitant murmur only due to the prolapse of the valve. The prolapse occurs due to the bulkiness of the valves due to myxomatous degeneration which also involves the chordae tendinae causing them to elongate to some extent. Like oversized sails, there is too much surface area and the upward momentum of the blood in systole causes them to "billow" up into the LA.
Normally, the leaflets, due to their attachment to the papillary muscles, get pulled down a little. The muscles elongate slowly at first, and then like a spring, they begin to pull the leaflets down. This allows the leaflets to convert the upward momentum of blood inwards since the attachment becomes taut. This causes the leaflets to approximate well and also reduces the size of the annulus due to the inward (and downward) pull of the leaflets (the leaflets are attached to the annulus at the margins). What happens when the bulky leaflets prolapse is that the force of this upward momentum continues to remain somewhat upwards. This causes a sudden elongation and then tautening of the papillary muscles (possibly the source of the click), like a sail filling too fast. This does not allow for reduction in the size of the annulus during systole, or proper approximation of the leaflets, instead letting blood regurgitate into the LA.
A fuller left ventricle allows the valve to shut properly, because now the papillary muscles are already somewhat taut, allowing their spring like action to work correctly. The slightly increased annulus size (before systole) may also allow the leaflets more space to approximate rather than prolapse. Hence the mitral valve apparatus functions better and the murmur and the click are reduced in intensity.
This article does a great job of explaining the mechanics, and also uses the sail analogy.
In valvular mitral regurgitation, the annulus may be excessively dilated, not allowing the leaflets to approximate even at peak systole, or there might be restriction in the motion of the leaflets preventing them from approximating. Thus increased LV size will exacerbate this problem, rather than alleviate it.
