THR vs THR REF - PMDG

thr 777Trying to understand THR mode coupled with FLCH. If I get it correctly, the aircraft will try to compute a given value of thrust (leading to a target VS) in order to get to the targetTHR – autothrottle applies thrust to maintain the climbdescent rate required by the pitch mode . mode changes to FLCH SPD. The FMC considers the MCP altitude setting