I am in favour of using the Arched (curved) finger approach because it relates well to finger strength,naturalness and efficiency of use, and avoidance of injury.
I refer students to the flat area between the centre of the fingerprint and the finger tip. It may not be so evident for people with thin fingers and/or very pointy fingertips. I bisect this area by the string. The two ways I approach the finger shape that will use this area are (1) resting your arched fingers on a table top to simulate playing the piano, and (2), to open a gentle fist as your left hand approaches the neck.
The closer you come to using the very end of your fingers (your finger tips?) the more vertically the last phalange becomes. Coming down too vertically on your fingertips tends to restrict the freedom and naturalness of the rise and fall of your fingers IMO.
So I use the following terminology. "Arched fingers keep their shape and rise/fall while flapping at the big knuckles, not bending and straightening fingers within their length (very stiff, slow and tiring). Forearm muscles cause the flapping motion. Alignment of the hand with the forearm through as straight a wrist as possible gives the best results and minimises the risk of injury. Pronating (bending) the wrist reduces the efficiency and strength of the flapping motion and increases the risk of injury. It is hard to avoid some pronation when fingering notes on the E string, especially when standing to play."
Holding your right forearm up in front of your chest can create a "bass neck" to demonstrate all the above.
I apologise for being so long-winded but "playing with tie tips of the fingers" allows too much room for interpretation and creation of bad habits IMO.
Cheers all,
DP