Let $k$ be a field. Let $C$ be an abelian $k$-linear category with a symmetric tensor product $\otimes$ and internal homomorphisms, such that $\mathrm{End}(1)=k$. Let $M$ be another $k$-linear abelian category, and let $$h:M\to C$$ be an exact, $k$-linear functor. If $C$ has arbitrary limits and $M$ is small, we can understand the endomorphism ring of $h$ as a ring object (a monoid) in $C$, as follows. It is the equaliser $$R := \ker \left( \prod_{m\in M}\mathrm{End}(h(m)) \xrightarrow{\quad u \quad} \prod_{m\to n}\mathrm{Hom}(h(m),h(n))\right)$$ where $u$ is "precomposition minus postcomposition". The given functor $h$ factors then canonically over the category of $R$-modules in $C$ $$M \xrightarrow{\quad\widetilde h \quad} R\mathrm{-Mod}_C \xrightarrow{\quad f \quad} C$$ where $f$ is the forgetful functor. My question is:

Is the functor $\widetilde h$ fully faithful?

For example, if $C$ is the category of vector spaces over $k$, then the answer is Yes. For this, $k$ does not even have to be a field. On the other hand, $C$ could be much larger, for example, the category of sheaves of $k$-vector spaces on a connected topological space. This is the case i am ultimately interested in.

Remark: The existence of limits in $C$ was just for convenience, without them, one can still view $R$ as a pro-ring object and consider $R$-modules. The hypothesis $\mathrm{End}(1)=k$ is essential if one wishes for a positive answer, because the category of modules $R\mathrm{-Mod}_C$ is always $\mathrm{End}(1)$-linear.

Remark: Also, the whole story smells like it was some variant of the Freyd-Mitchell theorem, but i don't see a concrete way to link it to that.