Kesubos 68a - Evaluating the Father's generosity

The gemara says that according to Shmuel who paskens like R' Yehuda in the Mishnah we evaluate the father's generosity and give the dowry accordingly, rather than simply giving 10% of his assets. Tosafos is bothered why by supporting the daughters i.e. food, we have a bare minimum (as in the mishnah 64b) and increase according to his wealth, but for the dowry we base it on his generosity. Tosafos answers that supporting the daughters is imposed on him by the tenai beis din, and therefore not pending on his generosity, rather it is an obligation based on his total assets. The dowry on the other hand is not imposed on him and therefore is based on his generosity. The Malei Haroim (back of gemara) asks, Tosafos answer is sufficient to explain why we we not evaluate the father's stinginess to lower his obligation of support, but perhaps we should evaluate his generosity to increase the level of support even if he is not that wealthy? He answers based on an important yesod in Tosafos 50b, that even acc. to Shmuel that we evaluate the father's generosity, that is only to decrease the amount to less than 10%, but we will never give her more than 10% even if he is extremely generous (the reason being is that chazal were careful not to abolish the inheritance rights of the son, so they limited the automatic dowry to be no more that 10% - unless the father stated explicitly otherwise). Therefore, the cap for the dowry is 10%, whereas the cap for support is assessing his assets, the only question was, why we don't take into consideration his stinginess to decrease support, and to that Tosafos answers that it is an absolute obligation not at all based on his level of generosity.