Without any additional info from the quote as to when chronologically during the 6 month campaign it was speaking of it isnt as easy so if you have that I would say add a post to expand on the quotation or when in the narrative it is set.

That said casualties between the often entrenched USMC and later Army units and IJA/SNLF units that attempted touse their so far very successful infiltration and bold light infantry tactics could be high. For instance at the first real confrontation between Japanese units attacking the USMC perimeter came on August 21 at the Tenaru River on the Eastern end of the US beachhead centered around Lunga Point and the airfield. Landing with an advance force from his regiment of about 900 men Col Ichiki attacked the US lines attempting to use the same playbook that had worked so well in China, The Philippines, and the rest of the DEI and Malaya though over some unfavorable ground including across open beach on one flank. He got hit men slaughtered for the effort after each wave was repulsed and Marine units supported by light armor counter encircled his position. For 775 or so Japanese dead the Marines lost about 40.

There would be other fights in the weeks and months to come on the island, and others with nearly as lopsided casualty rates, but the Tenaru stands out as the first time that truly prepared and ready US and IJA forces met during what would be the first in 3 years of a progressive counterattack by the Allied Powers in the South and Central Pacific.

Not quite the proportion described but not far off given how difficult sometimes casualty estimates could be and how often they could be wildly inaccurate.