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

for ie in range(int(input())):
    n=int(input())
    l=[int(i) for i in input().split()]
    c=0
    if len(set(l))==1:
        print(-1)
    else:
        for i in range(len(l)):
            if c==0:
                if i==0:
                    if l[i]>l[i+1] and l[i]+1>max(l):
                        c=i
                        continue
                if i==len(l)-1:
                    if l[i]>l[i-1] and l[i]+1>max(l):
                        c=i
                        continue
                
                if l[i]>l[i+1] or l[i]>l[i-1]:
                    if l[i]+1>max(l):
                        c=i
                        continue
                        
                    
            else:
                break
        print(c)