Assuming the 'artillery bunker' was on a small hill on the shore of the Serebryanyi Stream then Finnish sources likely agree with that part of the statement statement (hill is called 'public school hill'). Another relevant map: http://digi.narc.fi/digi/view.ka?kuid=4961514 p.592, '11.K:n alkuperäinen tavoite' (original objective of 11th Company) is the stream (Serebryanyi) and '11.K:n uusi tavoite' (new objective of 11th Company) that includes the 'public school hill'. From same document (online version) p. 579-580 (which are also p. 28-29 of III/JR6 war diary - same as 3rd Battalion of 6th Infantry Regiment) -   
4.9. ...Regiment's commander gave the order to advance to the stream 1/2 km north of N. Beloostrov in the direction of Aleksandrovka0900 Stiff resistance but the objective was reached by 1100 with support of the artillery and infantry heavy weapons. At this time it was noticed that a small hill (referred to in the source as 'public school hill') just south of the stream dominated the nearby areas and had to be taken as well.1500 New objective taken.
From same source, order by the commander of the 18th Division - http://digi.narc.fi/digi/view.ka?kuid=4961148 (p. 206-207) defines the front line on 4 September 1941 after that attack by the III/JR6 as follows:
3. Our regiment (excluding I/JR6) mans the 'Aleksandrovka section' (of the front line)... ...Edge on the right: Begins from Rajajoki (River Sestra) at roughly 1 km north of the railroad bridge and following the stream east from there...
So according to both to the war diary of the Finnish battalion (3rd Battalion of the 6th Infantry Regiment) responsible for the direction just north of N. Beloostrov and according to the war diary of its' parent unit, or the 6th Infantry Regiment, the Finnish front lines did not run further to the south from the stream in question (Serebryanyi) than extending to cover the 'public school hill'. And run 1/2 to 1 km north of the N. Beloostrov on the 4 September 1941 following the Finnish attacks. -