1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

test=int(input())
while test>0:
    n=int(input())
    a=list(map(int,input().split()))
    m=max(a)
    ans=0
    flag=0
    if(len(set(a))==1):
        flag=1
        print("-1")
        
    else:
	    for i in range(1,n-1):
	        if(a[i]>a[i+1] or a[i]>a[i-1] ):
	            if(a[i]==m):
	                flag=1
	                ans=i+1
	                print(ans)
	                break
	                
    if ans==0 and flag==0:
	    if a[0]==m:
	        ans=1
	    elif a[n-1]==m:
	        ans=n
	    print(ans)
    
        
    test-=1