Let's see, comparing the current Lunatic record replays after stage 3 to their final scores...
[monospace]Game: Stage3 score -> Final score (ratio) Player (replay name), shot type
EoSD: 302,882,650 -> 698,078,330 (2.30) 稼符一族 (ichizoku), ReimuB
PCB: 402,159,380 -> 3,174,824,650 (7.89) ナヤ (NAYA), SakuyaB [this is the highest non-TAS PCB replay I could find]
IN: 1,470,854,270 -> 6,609,993,580 (4.39) Alan (Depre), Youmu
MoF: 332,833,110 -> 2,214,529,240 (6.65) 名前の無い怪物 (Nanashi), MarisaB
SA: 286,726,930 -> 5,036,683,530 (17.57) ごぼう (gob), ReimuA
UFO: 304,400,980 -> 3,293,411,120 (10.82) アイスプライス (E-Splice), SanaeB
TD: 389,030,890 -> 3,747,775,430 (9.63) ひなぶ (7b.374), Youmu
DDC: 450,700,250 -> 2,045,748,300 (4.54) UKT, SakuyaB
[/monospace]
...It's a bit complicated.
Even ignoring some with clear reasons to be outliers (EoSD because it doesn't have PIV, MoF because its PIV caps early on Lunatic, and DDC since its record still isn't very optimized), the stage 6/stage 3 ratio still has quite a range.
I think the factor may be lower in LoLK than average, too, since much of the score comes from graze, which doesn't increase over the course of the game like PIV does.
However, none of the other games except IN even reach 500 million in stage 3, which predicts an above-average total score.