The hydraulic fluid is non compressible. Any dispacement in the MC is transferred to the brake calipers in a precise manner. You can lose dispacement by air in the system (gases are compressible) and balooning flexible hoses.

I do not believe there is any circulation in the brake system, there is no loop for that effect, the calipers are dead ends. Even if there were a loop, then we'd be talking about heat differentials like in gravity fed central heating systems, or we'd be looking for a circulating pump somewhere. The only way to flush the fluid from the hoses is to push it out through the calipers or suck it up to the reservoir somehow.

I have my reservation that drawing from the bleed valve renews the fluid in the caliper's piston chamber. There could be a "stream" where the new fluid travels from the brake hose to the bleed valve leaving the rest of the fluid almost intact. A better method might be to drive the piston all the way back , thus emptying the caliper of fluid, and keep it in that position untill you flush the hoses/caliper . But I think even that method leaves a lot of fluid inside the caliper unchanged.