The DCA strategy is a consistent way of accumulating Bitcoin gradually with as little as your discretionary income either every weeks or months while the lump sum is using huge amount of money to accumulate Bitcoin like for example you can win a lottery big amount and decide to use all or a very big amount of money to accumulate Bitcoin.
You can still use little amounts to lump sum into bitcoin and not necessarily a huge amount, let's say for example you got a bonus from work or you were gifted some money by a friend and decided to put everything into bitcoin, then you just lump summed with the extra funds you received, this doesn't have to affect your consistency in buying and holding bitcoin, it is still very possible to combine the both lump sum and DCA within your buying period if such extra funds surfaced therein.
But why do you want to lump sum with a little amount of money, what then happened to buying through the DCA where you can feel more comfortable, I think that is a wrong choice from someone who is just starting to buy bitcoin, there could be a situation where you have to buy in large quantities when you have enough availability of discretionary income then you can approach the lump sum, but I think its more reasonable to lump sum when you have enough discretionary income where you can buy bitcoin in large quantities and buy in bulk, the best thing you can do as a beginner who have a small amount of money is endeavor to approach buying through the DCA techniques which is more sustainable as a beginner.
Honestly speaking I dont see any reason to why I should combine both DCA and lump sum, when I can just buy bitcoin more comfortably through the DCA, there are individuals who have enough discretionary income they still dont buy through the lump sum they appreciate buying through the DCA, Im not saying any techniques is bad, it all depends on your approach.
Personally I prefer buying through the DCA and DCA is the best technique for me comparing all other techniques.