The Rosh infers from the gemara that a chazaka on one field will not work for a field that is located elsewhere, unless it is paid for in advance, that for a neighboring field the chazaka will work even if it hasn't yet been paid for (this assumption can be debated, because the sevara of "sadna d'arah chad hu" seems to suggest that there is no difference at all between neighboring fields and fields in different places). The Rosh suggests that chazaka would even work in the absence of shtar, even in a place where it is customary to write a shtar. Why is chazaka more powerful than kesef, namely that kesef does not work in a place where it is customary to write a shtar, yet chazaka will work even in a place where it is customary to write a shtar? The Rosh answers that kinyan chazaka is stronger than kesef because an action is being done in the "גוף הדבר", similar to meshicah which works even without kesef because the action is being done to the object itself.
The suggestion of the Rosh seems difficult to accept. The rationale for kesef not working in place where is is customary to write a contract is not a weakness in the kinyan, rather there is an unspoken assumption that the buyer and seller were expecting the contract to make the kinyan (that is why if they explicitly stated that the kesef should work without a shtar, it works as the gemara says 26a). So, why should chazaka being "stronger" make a difference, since the issue is not about the ability of the kinyan to work, rather about the intent of the kinyan to work?
I would like to suggest that the Rosh is making a simple distinction between kinyanim where the kinyan is merely in the act, and kinyanim that demonstrate ownership. Kinyanim like kesef and chalifin which are merely an act that the Torah considers valid to be a kinyan, but do not inherently demonstrate ownership, are not able to work when the expected act of kinyan is to use a shtar. However, when one is using a kinyan such as meshicha or chazaka which are methods of demonstrating ownership, the da'as of the buyer and seller would presumably be that demonstration of ownership works even in a place where the act of kinyan would demand a shtar.