In contemplating the holiness of God man develops more quickly than he does in his ability to conform his life to the commandments. Hence the impression that the distance between us and God continually increases.
This is what is so humanly frustrating about contemplative prayer. We can never "get anywhere" that we can understand or measure, and the further we do in fact get the greater the difference we perceive between ourselves and Jesus, whom we're called to resemble (1 Corinthians 11.1).
The only way out of thinking of this as a law of diminishing returns is absolutely to give up thinking of being rewarded for, or "getting anything out of", prayer, "for [we] have died, and your life is hidden with Christ in God." (Colossians 3.3)
I wish I could say it gets easier. It may do, eventually - though somehow I doubt it - but if it does I'm certainly not there yet!