The Impact of the contact surface
There are several drippers on the market with different designs, mainly with different grooves and shapes that provides different filter sits and fittings, these deigns,and groves mainly modifies the contact surface between the filter and the dripper, creating hair channels between and providing different extraction drawdowns and beverage filtrations (by pass).
In general terms a combination of a dripper + a filter with lower contact surface (a combination where the filter only has a very low contact with the dripper or dripper groves) provides a faster extraction drawdown and a higher by pass effect (let the pass of fluid with different levels of coffee particles extraction in to the mug), on the other hand a more contact surface between the filter and the dripper slows downs the drawdown of the extraction due to the less air circulation between the elements and the reduction of the bypass effect.
The drawdown fluid also changes depending on the filter contact surface, becoming more sensitive to the pours and water pressure once the contact surface is lower, and more regular and constant with more contact surface.
In our opinion, there’s not a better or worse combination, each one provides different results. But each one needs to be used depending on the target expected extraction. Less contact can provide fast flow and sharp results and more relevance to the pouring technique and recipe, and more contact can offer more and round developments.