B737 Captain reported being high on the crossing restriction at PERKN and MEEGO while on the CAVLR6 STAR into IAD and believes the STAR may be built too steep for the aircraft.

Narrative

We were level at FL220; and were given a descend via the CAVLR6; landing south. Autopilot was ON; autothrottles engaged; LNAV and VNAV PATH were engaged; and 4;000 feet was set in the altitude window. Approximately 1.7 miles prior to PERKN; the throttles reduced to idle; and the airplane started to pitch down to start the descent. I clicked off the autopilot as quick as I could; but we had descended to around FL21.7. I pitched up and climbed back up to FL220; and we crossed PERKN at approximately FL220. As we crossed PERKN; we dropped into VNAV SPD; because the airplane thought it was too high for the next crossing restriction; which is an altitude window to cross KHOOD between FL220 - 14;000 feet. As we crossed over PERKN; and we were in a more steep descent than usual to get back to the path; I reengaged the autopilot and deployed the speed brakes. We eventually got back to the VNAV PATH; but then as we got to MEEGO; with the autopilot ON and in VNAV PATH; the airplane also descended through the 11;000 feet crossing restriction at MEEGO; this is the first time I have had an airplane bust the crossing restriction at MEEGO too. Again; I clicked off the autopilot and slowed the rate of descent. I then reengaged the autopilot; and we made the speed and crossing restriction at CAVLR. I have had numerous airplanes bust the altitude at PERKN; but not MEEGO; until today. Today we had about a 70-kt. tailwind at PERKN; which is actually not too strong. I understand the FMC is a tool for us to use and that we still have to monitor the aircraft performance; but I have not seen altitude busts on a continuous basis more than I do at PERKN. I guess this is my little topic to investigate to see if we can get this resolved somehow.Again; my theory is that this STAR is just built too steep for the 737; and/or the FMC is looking at crossing KHOOD at 14;000 feet instead of a higher altitude within the window of FL220 - 14;000 feet. If the FMC looks at crossing KHOOD around 18;000 - FL200; then I don't think it would have such a steep descent after PERKN; and therefore not think that it has to start down prior to PERKN. Again; I am very familiar with this STAR.These two altitude busts were not done intentionally and I am hoping to bring this to the correct person's attention to see if there can be a fix for this STAR. I have filed numerous reports for this situation where; even though the FMC is programmed correctly; the autopilot is ON; autopilot engaged; in LNAV and VNAV PATH; the airplane still starts down prior to PERKN; or if already in the descent; it does not cross PERKN at the published FL220.