Silicone hoses are advantageous because they are light, but they are also relatively fragile; you have to use special (expensive) hose clamps as conventional clamps will compromise the hoses.
For that reason (and also because they are extremely expensive), I use high-quality rubber hose exclusively. It sounds like your problem is that your hard pipe is slightly undersized relative to the hose that you have. You can probably special-order hose that is slightly smaller, but perhaps a better solution is to expand the pipe somewhat.
Harbor Freight sells tailpipe expanders, which do a terrific job at this. I recently helped design a completely custom cooling pipe system for a Pantera that used a modern Mercedes remote thermostat bypass arrangement (unnecessary complexity in my view, but the owner really wanted it). This called for a mix of metric and standard size pipes, which was somewhat problematic when it came to hose selection.
I was able to spend an hour or so in my neighborhood NAPA finding various hoses with the proper bends, including tapered hoses that were larger at one end than at the other. But the final solution for a perfect fit was to expand a few of the pipes so that the hoses were a tight fit.
Here's a direct link to the expander tools, which come in three sizes:
Harbor Freight Tools
Cheers!