matzah ashira on Erev Pesach

Pesachim 99 tells us that a meal may not be eaten from close to mincha time until nightfall on Erev Pesach. Tosfos is bothered by the Mishna codifying what should be practically obvious. One cannot eat a meal because there is nothing to eat! Chameitz is prohibited from mid-day, and the Yerushalmi tells us that matzah may also not be eaten on Erev Pesach – what could this prohibited meal possibly consist of? Rabeinu Tam answers that this diyuk proves his contention that it is permissible to eat matzah ashira (what for us commonly is egg matzah) on Erev Pesach.

The reason for the restriction on eating Erev Pesach seems to be a dispute among the Rishonim. In yesterday’s post I cited the Rambam’s explanation (Chu”M ch 6) that matzah may not be eaten on Erev Pesach so that the mitzvah of eating matzah at night is distinctive (heker). Rashi and Rashbam explain that the reason is hiddur mitzvah, so that the matzah consumed at night is eaten with a full appetite (teyavon).

I don’t understand R’ Moshe Shternbruch’s suggestion in Moadim u’Zmanin (notes at the end of last volume) that whether or not Rabeinu Tam’s heter to eat matzah ashira is correct depends on this dispute. He writes that according to the Rambam that matzas mitzvah requires a heker, matzah ashira, which looks for the most part exactly like regular matzah, should be prohibited on Erev Pesach. However, according to Rashi, since matzah ashira tastes significantly different from regular matzah, eating matzah ashira would not diminish one’s appetite for regular matzah and therefore not be a problem.

Couldn’t one make exactly the opposite argument? Perhaps the difference in taste between matzah ashira and regular matzah is sufficient heker between the two and matzah ashira is permitted even according to the Rambam. And perhaps according to Rashi since matzah ashira is satisfying and fills a person up when eaten it should be avoided on Erev Pesach to perserve one's appetite for matzas mitzvah. Tzarich iyun for me on this one.