This sensation seems essential to a truly satisfying ejaculation. Is there any way to help make this a part of every ejaculation, or is it the luck of the draw?
Most males do indeed equate orgasmic pleasure with the quantity of semen ejaculated. My main suggestion is to stimulate yourself for as long as possible (delaying orgasm) before ejaculation. When you're heavily aroused your body secretes more of the fluids that make up an ejaculation, and they tend to build up. When you finally ejaculate, you'll expel more semen, and it will feel better. Also, drinking lots of water an hour or so before the session can help increase the ejaculate volume.
For more tips on delaying orgasm, see the JackinLibrary article Masturbate to Practice for Sex.