To get optimal damage from abyssal damage mods you want one(1) module with high Rate of Fire (RoF) and the rest to be high Damage Multipler (Dmg). You want the focused stat as high as possible while having minimal losses to the other stat. This is a result of how EVE does decaying returns.

Notice the percentages on these mag stabs: even with maxed gunnery skills they do not meet the requirements for a Kronos bastion badge. The example magstabs are shown below.

Instead of maximizing the percentages on all 3, each of these modules is either high Rate of Fire and low damage *OR* high damage and low RoF. Even though the percentages on these mag stabs are lower than the above examples, they create higher total DPS due to focusing on one stat each.

For Paladins, use one high RoF and three high damage modules.

As you can see the second set of focused modules, even though they are a 27.5%, 27.8% and 28.9%, will meet the 3900 dps requirement for the Kronos. Meanwhile the ones chosen based on higher percent alone at 28.9%, 29% and 29.1% only do 3893 DPS and are hence not enough. Because modules that only have one stat high tend to be considered less valuable, you can save a lot by buying focused modules.

A note on Vindicators: Because the Vindi has neither the burst aerator (increases RoF) nor a bastion module it is much less penalized for stacking RoF. As a result optimal abyssals for a Vindi is 2 high RoF and 2 high Dmg modules.