Keeping funds at hand to buy when the price of bitcoin dips is not lump sum but buying at the dip. Don't get it twisted, lump sum is when you have your bonus and use the money to buy bitcoin right aware regardless of the price of bitcoin. Like what you said there's nothing bad in splitting the funds in two or three parts, but if you don't buy right away with one part, you haven't lump sum.
Actually, some folks misunderstood buying at a DIP and lump summing. Buying at a DIP means keeping a discretionary income while waiting for the price of bitcoin to fall before buying but lump summing is simply what we call an ''all in''. An amount you have kept to invest at once probably without investing further amount again but only leave your investment to grow in the long term. @Frankolala, you sound a bit contradictory because for someone who wants to lump sum, there is no need of splitting funds again except for someone who want to start investing while keeping some amount to buy when a DIP occurs of which it can't be regarded as lump summing. Though an investor can still decide to split their discretionary income into three parts for DCA, lump summing and buying at a DIP.
You are actually right though they have a similarity which is buying and then one of the difference between these two strategy or method of accumulating Bitcoin is that, an investor can actually lump sum whether dip or not but an investor who uses the buy Dip method can only invest or buy when there is downtrend in the market. However, it will be more advantageous for an investor to buy during the Dip because they are going to accumulate more figure of Bitcoin compared to when there's no Dip. And again lump summing doesn't mean an investor won't continue his investment again off course they will that is if after lump summing they still have the capacity as a matter of fact I have seen someone who has lump sum and still continue with the DCA method which is very strategic and I believe with little or no time his portfolio will be great and also I think that is the fastest way or approach to build our..., only if one have the capacity.