gezel on less than a perutah

The gemara (Sanhedrin 59) writes that there is never a case where something is assur for a ben noach but permitted for a yisrael.  Mitzvos raise the bar on what we can or cannot do, they don't lower it.  Asks the gemara: what about stealing less than a perutah, which a ben noach is chayav for but not a yisrael?  Answers the gemara: התם משום דלאו בני מחילה נינהו.  

Rashi explains:  שאף ישראל נצטוו על הגזל אלא שפחות משוה פרוטה אינו נחשב גזל בעיניהם שעוברין על מדתן שרחמנין הן ומוחלין על דבר קל אבל בני נח אכזרים הם  A yisrael in theory is also chayav on gezel of less than a perutah, but we are nice guys and are mochel on such a trivial amount.  The beni noach are sticklers and they are makpid, so they are chayav.

When the Rambam in the beginning of hil geneiva quotes the issur of stealing even less than a perutah, the Magid Mishne explains: דין שוה פחות מפרוטה בממון כדין חצי שיעור באיסורין.  The shiur of the issue gezel is a perutah; less than that is an issur of chatzi shiur.  (Agav, there are shitos that hold that chatzi shiur only applies by issurei achila.  This M"M clearly disagrees).  If so, the reason why a ben noach is chayav has nothing to do with mechila or no mechila.  The reason why a ben noach is chayav is because, as the Rambam writes in hil melachim (9:10) שלא ניתנו השיעורין אלא לישראל בלבד, the concept of shiurim was given only to yisrael and not bnei noach.  A yisrael is exempt from the mitzvah of hashava, returning the stolen goods, because the amount is less than the shiur (this assumes there is no din of chatzi shiur on a mitzvas aseh); the same is not true for a ben noach for whom there is no threshold of a shiur.

The Minchas Chinuch (130:4) has a few nafka minos between these explanations:

1) gezel from a katan - according to Rashi, a yisrael should be chayav to return the money because a katan cannot be mochel.  The same would be true if the nigzal openly declares that he is not mochel.  However, according to the M"M, the ganav would not have to give the $ back because it is less than the shiur for the mitzvah of hashavah.

2) tziruf - according to Rashi, even if you steal multiple times, so long as each act of theft was on less than a perutah, the owner is mochel on each theft independently.  According to M"M, the owner is never mochel, so if the sum total of all the thefts adds up to more than a perutah, it must be returned.

3) change in value - according to Rashi, once there is mechila, the stolen goods belong to the thief even if the value later goes up.  According to M"M, there is never mechila, so if the value of the stolen goods becomes greater than a perutah, it must be returned.

4) kiddushin - if you put together the stolen amount with more $ and use it to be mekadesh a woman, according to Rashi the kiddushin is chal since there was mechila and the thief owns what was stolen.  According to the M"M, not.   

5) lachem - the MG"A (637:3) quotes the Yeraim that even if gezel aku"m is mutar, it is not lachem, so you should not steal an esrog from a nochri.  This fits well according to M"M that there is never mechila.  But according to Rashi, if gezel aku"m is mutar, then the aku"m probably gives up hope of getting his esrog back since he has no legal recourse, and so would be mochel.