Does presence of alkyl groups on alpha carbon increase yield of alkane in Kolbe's Decarboxylation? We know that, during the synthesis of alkanes by Kolbe's Decarboxylation reaction,
the reaction proceeds via a free radical $\ce{R.}$ at the anode.

So, an alkyl group, say methyl, when substituted at the alpha carbon will increase the yield of alkane since the radical is stabilized by hyperconjugation. But my book states that the presence of alkyl group on alpha carbon decreases the yield of alkane. Why is it so?
I have done some electrosynthesis work using the Kolbe reaction, what I found was with straight chain carboxylic acids that my platinum anode was quickly fouled.

When I had some branching at the beta site, I had much less electrode fouling and I got a good yield of my alkane.