Not "compulsion", but obedience. Obedience is an act of free will. Yes, absolutely, one gains more merit from obedience than works undertaken of one's own will. Submission of the will is the greatest mortification.
You really should stop posting.
If you
freely choose to do a
more difficult "penance" than what you are compelled to do by a Church precept, you will gain more merit than if you obediently follow a Church precept to do the same work. Your freedom to encuмber yourself to do something more pleasing to God than is required by precept, is what Jesus's moral teaching is all about.
This is why the evangelical counsels are voluntary and not forced on all Catholics. Those counsels are the "better path," but one gains more merit ("to be perfect," Matthew 19:21) because of the choice and the freedom to choose. Lay Catholics are held to a lower standard (Matthew 19:16), i.e., to simply "keep the Commandments."
We don't have a choice to keep the Commandments, we are compelled under pain of mortal sin to keep them. We do have a choice to voluntarily bind ourselves to the evangelical counsels on our quest to "be perfect." Similarly, with fasting/abstinence, by
choosing the more difficult penance, when we are not compelled by precept to do so, we will gain more merit.
I promise to stop posting after you learn Catholicism 101. Deal?