Simple answer: Yes and No.......
The concentric coil has the potential to go deeper then a DD but at its maximum depth it covers less area. This is because it has a cone shaped field and if you imagine a the tip of the cone being a lot smaller then the coil size (base of cone) you can see how easy it would be to miss targets. The DD is more like a blade shape - narrow but the length of the coil almost to its maximum reach and you are sweeping the field through the soil like a wiperblade on a windscreen.
Also the concentric will reach deeper in non-mineralised soil but the DD handles minerals better.
You got your finds today not because of the equipment but because you clicked onto digging the faint targets. I don't think changing coil type would improve this much, but changing coil size will. Standard rule of thumb is a good detector will reach at least as deep as the coil is long, thus a bigger coil will mean deeper targets (but you will get more masking from junk). Reckon you would be better to slow down and overlap your existing coil more listening out for those faint signals.
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